The present invention relates generally to load singulation systems, and more particularly, to a load singulation system made up of an array of similarly configured cells each having an individually operable actuation system.
Load manipulation devices are used for moving and positioning loads such as parcels, cartons, packages, or industrial parts. These devices may be used, for example, by mail processors, package handlers, or manufacturers. Conventional load manipulation devices include conveyor belts and robotic manipulators. Conveyor belts are well suited for moving large objects over long distances but lack the ability to displace objects in multiple directions and to orient objects. Robotic manipulators are able to precisely position and orient objects but are limited by strength, reach, and the need for large unobstructed workspaces.
Programmable load manipulation by an array of actuators has been proposed to overcome some of these drawbacks. United Kingdom Patent Application No. 2,259,900 describes a hardware platform comprising a set of transfer stations juxtaposed to form a matrix. The matrix is composed of identical platforms of a regular shape (e.g., triangular, square). Each platform contains the appropriate load-motion hardware such as a roller, conveyor belts, and multi-directional (i.e., horizontally and vertically) vibrating surfaces. The disclosed systems have numerous disadvantages. For example, the required hardware for each platform is complex (e.g., multiple degrees of motion freedom is required) and expensive to build and maintain. The system's reliance on bearings reduces the expected operating life of the system, since bearings (sliding surfaces) wear easily under repetitive motion. Moreover, platforms based on a vibrating surface configuration requires simultaneous vertical and horizontal vibration which requires driving hardware to achieve vibration in two planes. In particular, driving a surface vertically requires an amount of energy which increases with the weight of the load.
Load manipulation with an actuator array is also disclosed in Parcel Manipulation and Dynamics with a Distributed Actuator Array: The Virtual Vehicle (J. E. Luntz, W. Messner, and H. Choset, Proc. IEEE Int. Conf. on Robotics and Automation (ICRA), pages 1541-1546, Albuquerque, N.Mex., April 1997) (hereinafter “Luntz et al.”). Luntz et al. disclose an array of cells consisting of a pair of orthogonally oriented motorized roller wheels. Each wheel is driven through a gear reduction by a DC motor. The system requires expensive actuators with rotational speeds that must be accurately controlled electronically. Because rolling involves both static and sliding friction, it also introduces an added complexity of control in manipulating loads precisely. Another drawback of this system is that rollers do not pack together well, leaving large gaps between adjacent rollers, which can lead to jamming and the accumulation of loose particles inside the array.
One class of load manipulators are load singulation systems. Load singulation devices are used to arrange articles such as packages, into a single file so that the packages can be fed to a sorter machine, for example. Load singulation devices are generally categorized as open-loop or closed-loop devices.
Open-loop devices are configured for induction, accumulation, selective delivery, and recirculation of loads. The devices include actuators or obstacles that interact with loads under a specified arrangement. For example, U.S. Pat. No. 5,769,204 discloses a device operable to simultaneously push a forward-flowing stream of unsingulated packages against a sidewall to form a single file row of packages. Packages that are blocked from contact with the wall arrive at an input section spaced away from the wall. These packages are recirculated back to the device's input by a conveyor which attempts to force the packages back into the incoming flow. One drawback to these systems is the open-loop recirculation and reinsertion of packages. When the input flow is very dense, as is common in postal applications, for example, reinsertion by open-loop trial and error mechanisms is very inefficient. As a result, the recirculation buffer often overruns, resulting in system jams or failures. Another drawback is the removal of loads failing to connect with the singulating wall, which may result in a jam at the exit port. Constant human intervention is therefore required to keep the device up and running.
Closed-loop singulation devices are characterized by algorithmic driven load motion. The algorithm draws on real time data collected on the location and orientation of the loads. The singulation function is achieved by selective energization of components of a multi-actuator system. Closed-loop systems incorporate different types of sensing devices (e.g., laser beams, proximity sensors, imaging devices) and actuators (e.g., liver rollers, conveyor belts, actuated fences, pick-and-place actuation device). The systems include various recirculation, buffering, and transferring functions. U.S. Pat. No. 5,372,238 discloses an example of a closed-loop singulation system made up of a number of different modules. Each module contains several live-roller actuators and is selectively activated to induct, reorganize, store, recirculate, and transfer loads according to an instantaneous load arrangement. Closed loop devices such as this typically include a combination of different types of modules. A disadvantage of these systems is that they are mechanically heterogeneous (i.e., each module has a different configuration or is made up of different parts) and complex, with many independent moving parts and specialized modules. This results in high building costs, difficult maintenance, and complex performance analysis.
Other singulation systems lack the ability to process a continuous incoming load stream (i.e., the system can only operate on discrete batches of packages). Continuous operation is desirable when the incoming flow is very dense or fed at varying speeds, since continuous flow devices typically continue to singulate processed packages during input starvation.